Cataplexy is the sudden, generally brief, loss of muscle tone with retained consciousness. It is usually triggered by strong emotions, like laughter, surprise or anger. Episodes of cataplexy triggered by laughter may involve only certain muscle groups, such as arms and legs (e.g., knees buckling), the head and neck (e.g., head dropping), or the face and jaw (e.g., sagging of the jaw, slurred speech, eyelid drooping). Complete collapse can also occur as a result of a variety of emotions.